BOSTON — Jayson Tatum underwent surgery Tuesday to repair a ruptured right Achilles tendon, ending his season and putting his availability for the 2025-26 campaign in jeopardy.

“No timetable is currently available for his return,” the Celtics said in a statement confirming the diagnosis, “but he is expected to make a full recovery.”

Tatum, the NBA’s highest-paid player and one of its most durable superstars, suffered the non-contact injury with three minutes remaining in Monday night’s Game 4 loss to the New York Knicks at Madison Square Garden.

While attempting to beat Knicks wing OG Anunoby to a loose ball, he fell to the floor, clutched at his right ankle and had to be carried off the court by Celtics staffers. President of basketball operations Brad Stevens stepped in to help guide his star player, who was unable to put weight on his injured leg, down the tunnel.

ESPN’s game broadcast then showed Tatum, face buried in his hands, being transported by wheelchair toward the visitors’ locker room.

Trailing by seven at the time, the Celtics went on to lose, 121-113, to fall behind 3-1 in the best-of-seven Eastern Conference semifinals.

“Obviously, you’re always worried about someone’s health,” Celtics head coach Joe Mazzulla said. “So the fact that he had to be carried off — he’s the type of guy that he gets right up. He didn’t. And we’ll know (Tuesday) exactly what it is, but yeah. I mean, it’s tough to watch a guy like him get carried off like that.”

Tatum’s injury left his teammates shell-shocked.

“I think tonight is tough,” a visibly emotional Jaylen Brown said at the postgame podium. “I think everybody’s kind of at a loss for words, just because, one, losing the game, but obviously the concern with JT. But we pick our heads back up tomorrow and go from there.”

“I mean, at this point, I’m concerned about Jayson,” Al Horford added. “That’s the most important to me. The game stuff, we’ll address it. But I’m just hoping that he’s OK.”

Since entering the NBA as the third overall pick in the 2017 draft, Tatum leads the league in games and minutes played, including playoffs, and ranks second in total points behind Milwaukee’s Giannis Antetokounmpo. He’s never missed more than 10 games in a season and didn’t sit out his first postseason game until last month, when a bone bruise in his wrist sidelined him for Game 2 of Boston’s opening-round series against Orlando.

Tatum is a six-time All-Star, and he almost certainly will be named to his fourth consecutive All-NBA first team when it’s announced later this month. Last season, after a half-decade of near misses, he helped propel the Celtics to their elusive 18th championship, leading the team in points, rebounds and assists during both the playoffs and the NBA Finals.

To extend their season and keep their bid for back-to-back titles alive, the Celtics now must win three consecutive games without their best player — and with a depleted supporting cast. Injuries hit Boston’s roster much harder this season than they did during last year’s title run, and several core rotation players have either missed time or been limited during the first two playoff rounds.

That list includes Brown, who’s battled a troublesome knee injury since before the NBA All-Star break in February, and starting center Kristaps Porzingis, who’s been slowed by symptoms from a lingering viral illness that have zapped his energy and impacted his availability. Both players struggled in Monday’s loss to the Knicks, during which the Celtics blew a double-digit second-half lead for the third time in the series. Starting guard Jrue Holiday (hamstring) and reserve wing Sam Hauser (ankle) each have missed three games this postseason.

Tatum was terrific before his injury, recording 42 points, eight rebounds, four assists, four steals and two blocks in one of the best all-around playoff performances of his NBA career.

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